During the differentiation (sporulation) of Bacillus subtilis many new proteins with developmental functions are made. Because it is generally not known how the synthesis for developmental proteins are regulated, we have investigated one of them, glucose dehydrogenase and its developmentally-regulated gene (gld) in detail. The nucleotide sequence of the gld gene and the flanking DNA has been determined. The glucose dehydrogenase structural gene (780 base pairs) and an open reading frame (855 base pairs) that precedes it comprise a sporulation-specific operon. The latter is an essential gene for differentiation because its deletion from the Bacillus subtilis chromosome prevents the cell from sporulating. The nucleotide sequences of the ribosome binding and putative promoter sites have been identified. The promoter and regulatory region of the operon are located in a 0.5 kilobase (kb) PvuI fragment of plasmid pEF1 which was constructed by inserting a 4.0 kilobase EcoRI DNA fragment containing the structural gene of glucose dehydrogenase into the Escherichia coli plasmid, pBR322. Preceding the glucose dehydrogenase operon is another gene that is expressed coordinately with the gld gene.